1. Field of the Invention
The present invention relates to an electrostatic chuck (to be referred to as an ESC hereinafter) used to chuck a substrate and a method of manufacturing the same.
2. Description of the Related Art
As shown in FIG. 1, in a conventional ESC, a conductive film 8 is buried in a polyimide resin sheet 4, and a DC power supply (not shown) is connected to the conductive film 8 via a connecting conductor 16, a feeder sheet 14, a connecting conductor 18, and a feeder pin 24. The sheet 4 is bonded to the upper surface of an aluminum susceptor 6. A feeder film 12 is buried in the feeder sheet 14. The feeder film 12 and the conductive film 8 are electrically connected to each other via the connecting conductor 16. The feeder film 12 and the feeder pin 24 are electrically connected to each other via the connecting conductor 18. Each of these connecting conductors 16 and 18 is formed by baking a conductive paste. An end portion of the feeder pin 24 is pressed against the connecting conductor 18 by a spring 22.
The susceptor 6 is constituted by a combination of several members. The susceptor members are designed to be separable to allow easy replacement of the sheet 4. That is, the end faces of the susceptor members are separated from each other, with a clearance 10 having a width of about 1 mm being provided therebetween.
If the atmosphere at the contact portion between the feeder pin 24 and the connecting conductor 18 is set in a vacuum or low-pressure state, a discharge may occur. In order to prevent this, a gas with a pressure near the atmospheric pressure is sealed in a space 70.
The processing temperature for a semiconductor wafer varies from a low temperature of -150.degree. to a high temperature of about +100.degree. depending on the type of process to be performed. The low or high temperature source is supplied from the susceptor base 20 side. In order to improve the heat transfer efficiency, a heat transfer gas (helium gas) at the atmospheric pressure or a pressure of about 10 Torr is introduced between the susceptor base 20 and the susceptor 6. In addition, this helium gas is introduced to the interface between the sheet 4 and a wafer W and to the interface between the susceptor 6 and the susceptor base 20, thus acting to improve the heat transfer efficiencies therebetween.
The sheet 4, however, partly expands upward to form a projection 28 under the influence of a pressure difference P.sub.1 between the process chamber side (almost vacuum) and the clearance 10 side (almost 1 atm).
In general, in order to allow the ESC to fully exhibit its function, the flatness of the sheet surface must be ensured to a certain degree or more to ensure a good contact with respect to a wafer. However, a height H.sub.1 of the above projection 28 is larger than a limit value, e.g., 23 .mu.m, beyond which a good contact cannot be maintained. Consequently, the ESC cannot fully exhibit its function.
In addition, when the temperature of the susceptor 6 is changed in accordance with the type of process to be performed, a portion of the sheet 4 is separated from the susceptor 6 because of the difference in thermal expansion therebetween. As a result, the helium gas leaks to result in an unstable process. Furthermore, the sheet 4 is degraded due to thermal deformation, leading to insufficient insulation. Such problems of gas leakage, a degradation in the withstand voltage characteristics or a dielectric breakdown of an insulating member, and the like are posed when a low-temperature etching process is performed with respect to a wafer to form a microscopic pattern on the order of half microns and quarter half microns.